1. Field of the Invention
The present invention relates to a primary radiator used for receiving satellite broadcasting, a low noise blockdownconverter (hereinafter referred to as “LNB”) using the primary radiator and a satellite broadcasting receiving antenna.
2. Description of the Background Art
A first conventional example of a so-called dual horn will be described. The dual horn includes two horns arranged close to each other to form a main body of a primary radiator. Specifically, a die-casting die is used to mold only the dual horn or the dual horn together with the main body in one piece (see for example Japanese Patent Laying-Open No. 11-041028). As shown in FIG. 9 for example, this conventional dual-horn primary radiator molded by die casting includes two horns 21a, 21b and double corrugated portions 22a, 22b. A second conventional example of the dual horn uses sheet metals of similar shapes to form one primary radiator (see for example Japanese Patent Laying-Open No. 2004-336154).
The first conventional example, however, lacks adaptability in that for example the shape cannot be changed after the horn is once fabricated, because the horn which is a casting is fabricated using a mold. In the case where the shape of the horn is to be drastically changed, a new mold has to be prepared, which means the investment cost increases. Further, the second conventional example has the problem that only one primary radiator can be formed using the sheet metals of similar shapes.